Process for the production of methanol and a composition suitable for use as a catalyst in said process

ABSTRACT

A process for the preparation of methanol by contacting CO and H 2  with a novel catalytic system formed by combining (a) a nickel salt having a pK a  &lt;4.70, (b) an alcohol, and (c) a hydride of an alkali metal or of an alkaline earth metal.

This is a division of application Ser. No. 175,027, filed Mar. 30, 1988,now U.S. Pat. No. 4,868,221.

FIELD OF THE INVENTION

The invention relates to a process for the production of methanol. Theinvention also relates to a novel catalyst composition.

BACKGROUND OF THE INVENTION

A process for the production of methanol is described in U.S. Pat.Specification No. 4,619,946, issued Oct. 28, 1986, which concernsreacting carbon monoxide with hydrogen in the presence of a catalyticsystem of the type NaH-RONa- nickel acetate in which R represents analkayl group having 1-6 carbon atoms. This catalytic system can be mademore active by "conditioning," involving contacting for a prolonged timewith a gaseous mixture comprising carbon monoxide and hydrogen at suchan elevated temperature and elevated pressure that a substantial amountof carbon monoxide and hydrogen is consumed for this "conditioning."

Another process for the production of methanol is described in Japanesepatent application publication No. 56-169,634, published Dec. 26, 1981,which concerns reacting carbon monoxide and hydrogen in the presence ofa catalyst comprising a nickel compound and an alkali metal alkoxide.

It is an object of the present invention to produce methanol in thepresence of a catalytic system having enhanced activity.

It is another object of the present invention to produce methanol in thepresence of a catalytic system that retains its activity for a longtime.

SUMMARY OF THE INVENTION

The invention provides a process for the production of methanol whichprocess comprises contacting a gaseous mixture comprising carbonmonoxide and hydrogen with a catalytic system prepared by combining thefollowing components:

component (a): a nickel salt of an acid having a pK_(a), measured inaqueous solution at 25° C., of less than 4.70,

component (b): an alcohol, and

component (c): a hydride of an alkali metal and/or a hydride of analkaline earth metal.

DETAILED DESCRIPTION OF THE INVENTION

The anion of the salt in component (a) may be derived from a greatvariety of acids having a pKa, measured in aqueous solution at 25° C.,of less than 4.70. It is preferred that the salt in component (a) is asalt of a carboxylic acid. Among these acids preference is given toformic acid and oxalic acid. Component (a) is most preferably nickelformate or nickel oxalate.

Examples of carboxylic acids from which component (a) may be derived aredicarboxylic acids such as malonic acid, dimethylmalonic acid, succinicacid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaicacid, phthalic acid, isophthalic acid and terephthalic acid. Thecarboxylic acids from which component (a) may be derived may containsubstituents, for example, alkoxy groups, particularly those having notmore than five carbon atoms, hydroxy groups, cyano groups and fluorine,chlorine, bromine and iodine atoms. Examples of such carboxylic acidsare glycolic acid, 2-hydroxypropionic acid, 3-hydroxypropionic acid,glyceric acid, tartronic acid, malic acid, tartaric acid, tropic acid,benzilic acid, salicylic acid, anisic acid, gallic acid,3,5-dichlorobenzoic acid, 3,5-dibromobenzoic acid, cyanoacetic acid,monofluoroacetic acid, difluoroacetic acid, trifluoroacetic acid andtrichloroacetic acid. Component (a) is not derived from acetic acid,having of 4.75, as the only acid. It is, however, not excluded from thescope of the present invention that component (a) contains anions of acarboxylic acid having a pK_(a) of less than 4.70 and also anions ofacetic acid.

A mixture of the above-mentioned salts may be used in component (a). Forexample, a mixture of a formate and an oxalate or a mixture of a formateand a benzoate can be used.

The salts in component (a) may contain crystal water, but are preferablyfree therefrom.

The alcohol of component (b) may be aromatic or cycloaliphatic but ispreferably aliphatic. Preference is given to alkanols, in particular tothose having in the range of from 1 to 20 carbon atoms per molecule.Among the latter alkanols those having in the range of from 4 to 12carbon atoms per molecule are preferred, because such alkanols can beeasily separated from methanol by means of distillation. Examples ofsuch alkanols are tert-butyl alcohol, tert-pentyl alcohol, hexanol,heptanol and alkanols having in the range of from 8 to 12 carbon atomsper molecule. Tert-butyl alcohol and tert-pentyl alcohol areparticularly preferred. Dihydric alcohols may also be used, for example,ethylene glycol, propylene glycol, 1,3-dihydroxypropane, 1,2-butanediol,1,3-butanediol, 1,4-butanediol, 2,3-butanediol or 1,2-pentanediol.Component (b) may also be glycerol.

Component (b) may be a mixture of alcohols, for example, of tert-butylalcohol and ethylene glycol or of tert-pentyl alcohol and1,4-butanediol.

Component (c) may be a hydride of lithium, sodium, potassium, rubidium,cesium, calcium, strontium, barium or magnesium. Preference is given tosodium hydride. The hydride may be added as such, but it has been foundthat the hydride may advantageously be added as a suspension in an inertdiluent, for example, a mineral oil, such as a heavy hydrocarbon oil,preferably a so-called white paraffin oil.

If desired, an alcoholate of an alkali metal or an alcoholate of analkaline earth metal may also be combined in the catalytic system. Thisalcoholate is preferably a sodium alcoholate or a potassium alcoholate.Among the alcoholates preference is given to alkoxides, particularly tothose having in the range of from 1 to 20 carbon atoms per molecule,such as sodium methoxide, sodium ethoxide, sodium propoxides, sodiumbutoxide, sodium isobutoxide, sodium tert-pentoxide and potassium2-methyldodec-2-oxide.

It has, furthermore, been found that the activity of the catalyticsystem can be further enhanced by a pre-treatment. According to apreferred embodiment of the present invention the catalytic system ispre-treated by contacting it for a prolonged time with a gaseous mixturecomprising carbon monoxide and hydrogen at such an elevated temperatureand elevated pressure that no substantial consumption of carbon monoxideand hydrogen takes place during the pre-treatment. Usually, a period inthe range of from 10 minutes to 5 hours at a temperature between 30° C.and 150° C. and a pressure between 5 and 100 bar is sufficient for thepre-treatment. The pre-treatment ends when the pressure progressivelystarts decreasing, which is a signal for formation of substantialamounts of methanol. Surprisingly, the present pre-treatment consumesvery little carbon monoxide and hydrogen but yet results in theformation of a catalytic system having a considerably enhanced activityfor the production of methanol. At the end of the pre-treatment thetemperature may be adjusted to the required reaction temperature, whichis a value at which substantial amounts of methanol are produced. Thisadjustment may be an increase of the temperature, but it is alsopossible that the temperature can be decreased. Such an increase ordecrease of the temperature will usually be over a range of 10° C. to50° C. It is, however, possible, that no adjustment of the temperatureis required at all, pre-treatment and methanol production being carriedout at substantially the same temperature.

The process according to the present invention may be carried out at atemperature and a pressure which are not critical and may vary withinwide ranges. Preferably, a temperature in the range of from 30° C. to150° C. and a pressure in the range of from 5 to 100 bar are used.

The process according to the present invention may be carried out withan organic diluent in which the catalytic system is present, at leastpartly, as a suspension. Suitably, a weight ratio of organic diluent tocomponent (a) in the range of from 0.1 to 5000 is used, but this weightratio may be lower than 0.1 or higher than 5000. The process accordingto the present invention is preferably carried out using a molar ratioof component (c) to component (a) in the range of from 0.5:1 to 100:1and, more preferably, from 1:1 to 50:1, but the use of molar ratiosbelow 0.5 and above 100 is not excluded. The process may be carried outusing a molar ratio of component (b) to component (a) which is notcritical and may vary within wide ranges, preferably in the range offrom 0.1 to 1 to 100 to 1.

Any inert diluent may in principle be used. Examples of suitablediluents are ketones, such as acetone, methyl ethyl ketone, methylisobutyl ketone, acetophenone, cyclohexanone and acetylacetone; etherssuch as anisole, 2,5,8-trioxanonane (also referred to as "diglyme"),diethyl ether, diphenyl ether, diisopropyl ether and tetrahydrofuran;aromatic hydrocarbons, such as benzene, toluene, the three xylenes andethylbenzene., halogenated aromatic compounds, such as chlorobenzene ando-dichlorobenzen; halogenated alkanes, such as dichloromethane andcarbon tetrachloride., alkanes, such as hexane, heptane, octane,2,2,3-trimethylpentane and kerosene fractions; cycloalkanes, such ascyclohexane and methylcyclohexane; nitriles, such as benzonitrile andacetonitrile; sulfoxides, such as dimethyl sulfoxide; sulfones, such asdiisopropyl sulfone, tetrahydrothiophene-1,1-dioxide (also referred toas "sulfolane"), 2-methyl-4-butylsulfolane and 3-methylsulfolane.Mixtures of two or more solvents may be used. Very good results havebeen obtained with ethers.

The carbon monoxide and hydrogen may be used as pure gases or dilutedwith-an inert gas such as a noble gas or nitrogen. The process accordingto the present invention may be carried out using a molar ratio carbonmonoxide to hydrogen in the gaseous mixture which is not critical andmay vary within wide ranges, suitably in the range of from 1:0.2 to1:20. The carbon monoxide and hydrogen may be obtained by partialoxidation of hydrocarbons, for example, of natural gas. The methanolproduced according to the invention may be used for a variety ofpurposes, for example, for the manufacture of synthetic gasoline, as afuel component and for the production of methyl tert-butyl ether.

The process according to the present invention may be carried outbatchwise, semi-continuously or continuously.

The invention also provides a novel composition prepared by combiningthe following components:

component (a): a nickel salt of an acid having a pK_(a), measured inaqueous solution at 25° C., of less than 4.70,

component (b): an alcohol, and

component (c): a hydride of an alkali metal and/or a hydride of analkaline earth metal.

Said novel composition may be used as a catalytic system in the processaccording to the present invention.

The ranges and limitations provided in the instant specification andclaims are those which are believed to particularly point out anddistinctly claim the instant invention. It is, however, understood thatother ranges and limitations that perform substantially the samefunction in substantially the same manner to obtain the same orsubstantially the same results are intended to be within the scope ofthe instant invention as defined by the instant specification andclaims.

The invention is further illustrated by means of the following Examples.Each experiment was carried out in a 300 ml Hastelloy C autoclave("Hastelloy" is a trade mark) provided with a magnetic stirrer. Thesodium hydride was used as a suspension in white paraffin oil containing80% by weight of NaH. The reaction mixtures were analysed by means ofgas-liquid chromatography.

COMPARATIVE EXPERIMENT A

The autoclave was charged under a nitrogen atmosphere with diglyme (50ml), nickel acetate.4H20 (10 mmol), sodium hydride (60 mmol) andtert-butyl alcohol (20 mmol), heated to a temperature of 45° C. withstirring and kept at this temperature for 2 hours. Then, a solution oftert-butyl alcohol (30 mmol) in diglyme (50 ml) was introduced into theautoclave, the autoclave was sealed and a mixture of 1 volume of carbonmonoxide and 2 volumes of hydrogen was admitted until a pressure of 45bar was obtained.

The autoclave was further heated to a temperature of 100° C. and thepressure was then kept at a value between 30 and 60 bar by introducingintermittently said mixture of carbon monoxide and hydrogen.

The pressure remained constant after 2 hours at 100° C. which indicatesthat the catalyst had lost its activity. At this moment the autoclavewas allowed to adopt ambient temperature and then depressurized. Thereaction mixture contained a black-green solid substance and 2.8 g ofmethanol and 0.3 g of methyl formate.

EXAMPLE 1

Comparative Experiment A was repeated with the difference that nickelacetate.4H₂ O (10 mmol) was replaced with nickel formate. 2H₂ O (10mmol) and that the temperature was kept at 100° C. for 5 hours insteadof 2 hours.

At the end of this period of 5 hours the pressure was decreasing whichindicates that the catalytic system had retained activity. The reactionmixture contained a yellow solid substance and 3.8 g of methanol; thepresence of methyl formate could not be detected.

Comparison of Example 1 with Comparative Experiment A shows that inExample 1 where nickel formate was used more methanol and no methylformate was formed and that the catalytic system had a longer life.

EXAMPLE 2

The autoclave was charged under a nitrogen atmosphere with diglyme (50ml), nickel formate.2H₂ O (10 mmol), sodium hydride (60 mmol) andtert-butyl alcohol (20 mmol), heated to a temperature of 45° C. withstirring and kept at this temperature for 0.5 hour. Then, a solution oftert-butyl alcohol (30 mmol) in diglyme (50 ml) was introduced into theautoclave, the autoclave was sealed and a mixture of 1 volume of carbonmonoxide and two volumes of hydrogen was admitted until a pressure of 45bar was obtained.

The autoclave was further heated to a temperature of 85° C. and kept atthis temperature for 2 hours in order to pre-treat the catalytic system.The pressure remained almost constant during these 2 hours whichindicated that almost no reaction took place.

The autoclave was further heated to a temperature of 100° C. and thepressure was then kept at a value between 30 and 60 bar by introducingintermittently said mixture of carbon monoxide and hydrogen.

The pressure was still decreasing after 3 hours at 100° C. whichindicates that the catalytic system had retained activity. At thismoment the autoclave was allowed to adopt ambient temperature and thendepressurized. The reaction mixture contained a yellow solid substance,13.5 g of methanol and 1.5 g of methyl formate.

Comparison of Example 2 where the catalyst had been pre-treated for 2hours at 85° C. with Example 1 where no pre-treatment had taken placeshows that the pre-treatment considerably enhanced the production ofmethanol.

COMPARATIVE EXAMPLE B

Example 2 was repeated with the difference that nickel formate.2H₂ O (10mmol) was replaced with nickel acetate.4H₂ O (10 mmol) and that thereaction was terminated after 4 hours at 100° C. instead of 3 hours at100° C.

The pressure decreased during the period of 2 hours heating at 85° C.which indicates that pre-treatment of the catalyst and/or methanolformation took place.

At the moment of termination of the experiment the pressure had obtaineda constant value which indicates that the catalyst had lost itsactivity. The reaction mixture contained 3.6 g of methanol and 0.4 g ofmethyl formate.

Comparison of Comparative Experiment B where nickel acetate was usedwith Example 2 where nickel formate was used shows that heating for 2hours at 85° C. in the presence of nickel acetate does not enhance theproduction of methanol.

EXAMPLE 3

The autoclave was charged under a nitrogen atmosphere with diglyme (50ml), nickel oxalate.2H20 (10 mmol), sodium hydride (60 mmol) andtert-butyl alcohol (20 mmol), heated to a temperature of 45° C. withstirring and kept at this temperature for 0.5 hour. Then, a solution oftert-butyl alcohol (30 mmol) in diglyme (50 ml) was introduced into theautoclave, the autoclave was sealed and a mixture of 1 volume of carbonmonoxide and 2 volumes of hydrogen was admitted until a pressure of 45bar was obtained.

The autoclave was further heated to a temperature of 100° C. and kept atthis temperature for 2 hours in order to pre-treat the catalytic system.The pressure remained almost constant during these 2 hours whichindicates that almost no reaction took place.

The autoclave was further heated to a temperature of 120° C. and thepressure was then kept at a value between 30 and 60 bar by introducingintermittently said mixture of carbon monoxide and hydrogen.

The pressure was still decreasing after 2.5 hours at 120° C. whichindicates that the catalytic system had retained activity. At thismoment the autoclave was allowed to adopt ambient temperature and thendepressurized. The reaction mixture contained a yellow solid substanceand 6 g of methanol.

COMPARATIVE EXPERIMENTS C AND D

Comparative Experiment A was repeated with the difference that nickelacetate.4H₂ O (10 mmol) was replaced with nickel acetylacetonate (10mmol, Comparative Experiment C) or nickel cyanide (10 mmol, ComparativeExperiment D).

In both cases, the reaction mixture contained a black-green solidsubstance and no methanol.

COMPARATIVE EXPERIMENT E

The autoclave was charged under a nitrogen atmosphere with diglyme (100ml), nickel acetate4.H₂ O (10 mmol) and potassium tert-butoxide-(60mmol), sealed and pressurized with a mixture of 1 volume of carbonmonoxide and 2 volumes of hydrogen until a partial pressure of hydrogenof 30 bar and of carbon monoxide of 15 bar was obtained. The autoclavewas heated to a temperature of 80° C., kept at this temperature for 2hours, then further heated to a temperature of 100° C. and kept at thistemperature for 3 hours. At the end of this period the autoclave wasallowed to adopt ambient temperature and depressurized.

The reaction mixture contained a black-green solid substance and 0.2 gof methyl formate and less than 0.1 g of methanol.

What is claimed is:
 1. A composition prepared by combining the followingcomponents:component (a): a nickel salt of an acid having an pK_(a),measured in aqueous solution at 25° C., of less than 4.70, component (b)an alcohol, and component (c) a hydride of an alkali metal and/or ahydride of an alkaline earth metal.
 2. The composition as claimed inclaim 1, wherein said salt in component (a) is a carboxylate.
 3. Thecomposition as claimed in claim 2, wherein said salt in component (a) isnickel formate.
 4. The composition as claimed in claim 2, wherein saidsalt in component (a) is nickel oxalate.
 5. The composition as claimedin claim 1, wherein said alcohol in component (b) is an alkanol.
 6. Thecomposition as claimed in claim 5, wherein said alkanol has in the rangeof from 4 to 12 carbon atoms per molecule.
 7. The composition as claimedin claim 6, wherein said alkanol is tert-butyl alcohol or tert-pentylalcohol.
 8. The composition as claimed in claim 1, wherein said hydridein component (c) is sodium hydride.
 9. The composition as claimed inclaim 1, which further comprises an alcoholate of an alkali metal or analcoholate of an alkaline earth metal.
 10. A catalytic compositionprepared by combining:(a) a nickel salt selected from the groupconsisting of nickel formate, nickel oxalate, or a mixture thereof; (b)an alcohol having from 4 to 12 carbon atoms; and (c) sodium hydridesuspended in a mineral oil;wherein said catalytic system is pretreatedby contacting with a gaseous mixture comprising carbon monoxide andhydrogen for a period of time ranging from about ten minutes to about 6hours at an elevated temperature and an elevated pressure at which nosubstantial consumption of carbon monoxide and hydrogen takes place.